Fort Shafter was built in 1905 and finished by 1907, making it the oldest military base on Oahu. It is built on former Hawaiian crown lands that were turned over to the U.S. after annexation. The base is named for Major General William Rufus Shafter who led the U.S. expedition to Cuba in 1898.


The barracks and officers' quarters were spread out around Palm Circle, an open green space ringed by Royal palm trees, and the base expanded from there. In 1914, a regimental-sized cantonment area was built where Richardson Theater now stands. The Hawaiian Ordnance Depot was built in 1917 as a separate post. Tripler General Hospital, which moved to its present location in 1948, used to stand where the highway intersection is now. In 1921, the Hawaiian Department was moved from a downtown hotel to the post.


Fort Shafter saw far fewer casualties during the attack on Pearl Harbor, however, than did the Navy and Marines; one soldier was killed by an errant Navy shell on post. During World War II, Shafter served as an anti-aircraft artillery post, but mainly as a senior Army command post for the Asia-Pacific theater.


In 1944, the Army Corps of Engineers built the "Pineapple Pentagon" in just 49 days, with conversion of barracks housing into offices and other headquarters facilities. The post remained the Army headquarters of the Asia-Pacific region until after WWII; the U.S. Army, Pacific (USARPAC) took over in 1947. In the 1960s, the building of the Moanalua Freeway split the base in two parts, but it survived the decreased activity post-Vietnam. Then, in 1974, the Army replaced USARPAC with two smaller groups, the U.S. Army Support Command, Hawaii, and the CINPAC Support Group. During the same year, Hawaii's Fort Armstrong Army Corps of Engineers' Pacific Ocean Division moved to Shafter.


A short time later, the Army redesignated over half its undeveloped land back to the state of Hawaii. In 1990, the headquarters once again became the USARPAC. Today, over 5,000 military, civilian, contractor and family members live and work at Fort Shafter.